For anyone using RO water, having a TDS meter is a very valuable quality assurance check on the water. This applies to both people with their own machines and those that purchase from a vending machine. Membranes eventually wear out and the water quality goes down. The TDS meter alerts you of this condition.

I understand the meters are inexpensive and they'll help you to know what's in your water. At some point I was tired of guessing about the water and I wanted to know. I live in an area where many homebrewers use the same water and send samples to Ward Labs and the numbers always come back the same or very, very close. I have sent my water for analysis twice and the numbers were right on. So I am comfortable with my source water but then this bulk RO water threw me a curve so I went with distilled. Very tricky to know what to add or how to treat when you don't know what's in the water and I'm convinced that water composition is one of the main keys to making stellar beer. Cheers.

For anyone using RO water, having a TDS meter is a very valuable quality assurance check on the water. This applies to both people with their own machines and those that purchase from a vending machine. Membranes eventually wear out and the water quality goes down. The TDS meter alerts you of this condition.

I also found that using an aquarium "hardness" detector worked well for me.

It's the "drops" kind that measure GH and KH. Every so often, I check it, and the KH is always one drop from my RO water, which means 16-17 ppm of carbonate hardness.

I happen to have a little aquarium, so I had that on hand.

__________________Broken Leg BreweryGiving beer a leg to stand on since 2006

For anyone using RO water, having a TDS meter is a very valuable quality assurance check on the water. This applies to both people with their own machines and those that purchase from a vending machine. Membranes eventually wear out and the water quality goes down. The TDS meter alerts you of this condition.

The $64,000 question then, is, at what point are the TDS too high? The carboy of RO water I just bought reads 8ppm, while the same water tested at 3ppm a few weeks ago. Is this a sign the membrane is wearing out, or does it seem like a reasonable amount of variation?

The $64,000 question then, is, at what point are the TDS too high? The carboy of RO water I just bought reads 8ppm, while the same water tested at 3ppm a few weeks ago. Is this a sign the membrane is wearing out, or does it seem like a reasonable amount of variation?

Excellent question and discussion here! I'm wondering what all I should be testing as I happen to work at a water treatment plant and we have a fully certified lab. I was intending on purchasing water from a supermarket vending machine setup.

The $64,000 question then, is, at what point are the TDS too high? The carboy of RO water I just bought reads 8ppm, while the same water tested at 3ppm a few weeks ago. Is this a sign the membrane is wearing out, or does it seem like a reasonable amount of variation?

There may be some variation in the RO quality, if the source water quality varies. But what you should monitor is if there is a consistent increase in TDS. Generally, TDS should hover in a narrow range. When it starts to climb, its then time to replace the membrane. By the time the TDS quadruples, its time to get that membrane replaced. This sort of monitoring is probably not to possible for brewers buying their water from a machine. But for those vending machine patrons, reconsider using their water if the TDS is above 50 ppm. 50 is pretty high for RO water.

Can I assume that source water with higher TDS and bicarb numbers are tougher on the RO equipment or might require the membranes to be replaced more often? If a grocery store RO dispenser was starting with very soft water vs. a machine that started with higher bicarb or TDS numbers... which machine would last longer/work better/be more efficient/be more likely to provide consistently good RO water? At this point I'm just always keeping my eye open for good prices on distilled water. Occasionally I see it for 69¢ a gallon and then I jump on it. Cheers.

Yes, higher TDS requires a higher water wasting rate to avoid fouling the membrane prematurely. Given that most home systems have a fixed wasting rate, the implication is that the membrane on a home system will be fouled more quickly with higher TDS water. However, TDS is not the whole story. The nature of the TDS also has an important effect. If the water has high Ca, Mg, or silicate which are more prone to forming scale, then the membrane is more likely to foul. If the water is low in those ions, then the system is likely to last longer. Using ion-exchange softened water does improve the life of RO systems.

There may be some variation in the RO quality, if the source water quality varies. But what you should monitor is if there is a consistent increase in TDS. Generally, TDS should hover in a narrow range. When it starts to climb, its then time to replace the membrane. By the time the TDS quadruples, its time to get that membrane replaced. This sort of monitoring is probably not to possible for brewers buying their water from a machine. But for those vending machine patrons, reconsider using their water if the TDS is above 50 ppm. 50 is pretty high for RO water.

Well I tested my store's RO water. It had no real measurable alkalinity or hardness (via titration), but it shows 82 TDS. Sigh. Not sure how important that is in the grand scale. If the hardness and alkalinity are knocked out, should I still care about TDS?

Well I tested my store's RO water. It had no real measurable alkalinity or hardness (via titration), but it shows 82 TDS. Sigh. Not sure how important that is in the grand scale. If the hardness and alkalinity are knocked out, should I still care about TDS?

Interesting. It occurs to me that an RO water machine is a great way to trick people into buying fancy water but it's really just tap water. Many times I stood there waiting for my 5-gallon bottle to fill thinking, "This is probably just f***ing tap water" which is why I eventually sent a sample into Ward. I wish I could help with the TDS but I'm not sure how it comes into play in brewing. I concentrate on the big 6 (Ca, Mg, Na, Cl, SO4, HCO3) and don't really look into the other stuff. The TDS in my source water is 264. Cheers.